Surface Segregation of Fluorinated Moieties on Random Copolymer Films Controlled by Random-Coil Conformation of Polymer Chains in Solution

Abstract

The relationship between solution properties, film-forming methods, and the solid surface structures of random copolymers composed of butyl methacrylate and dodecafluorheptyl methylacrylate (DFHMA) was investigated by contact angle measurements, X-ray photoelectron spectroscopy, sum frequency generation vibrational spectroscopy, and surface tension measurements. The results, based on thermodynamic considerations, demonstrated that the random copolymer chain conformation at the solution/air interface greatly affected the surface structure of the resulting film, thereby determining the surface segregation of fluorinated moieties on films obtained by various film-forming techniques. When the fluorinated monomer content of the copolymer solution was low, entropic forces dominated the interfacial structure, with the perfluoroalkyl groups unable to migrate to the solution/air interface and thus becoming buried in a random-coil chain conformation. When employing this copolymer solution for film preparation by spin-coating, the copolymer chains in solution were likely extended due to centrifugal forces, thereby weakening the entropy effect of the polymer chains. Consequently, this resulted in the segregation of the fluorinated moieties on the film surface. For the films prepared by casting, the perfluoroalkyl groups were, similar to those in solution, incapable of segregating at the film surface and were thus buried in the random-coil chains. When the copolymers contained a high content of DFHMA, the migration of perfluoroalkyl groups at the solution/air interface was controlled by enthalpic forces, and the perfluoroalkyl groups segregated at the surface of the film regardless of the film-forming technique. The aim of the present work was to obtain an enhanced understanding of the formation mechanism of the chemical structure on the surface of the polymer film, while demonstrating that film-forming methods may be used in practice to promote the segregation of fluorinated moieties on film surfaces.

Comb-like polymer blends of poly(oxyethylene)s with CH3-terminated and CF3-terminated alkylsulfonylmethyl side chains: Effect of terminal CF3 moiety on the surface properties of the blends

“…In general, perfluorinated species of fluoropolymers tend to segregate onto the outer surface due to their low surface energies [29,30]. Therefore, fluoropolymers have often been studied as surface-modifying additives of polymer blends, in order to control their surface properties [31].…”

Probing polymer surfaces and interfaces using sum frequency generation vibrational spectroscopy - a powerful nonlinear optical technique

“…Wang and his colleagues studied the surface strucutures of random copolymers composed of methacrylates and fluorinated units solidified from the solution using SFG and other techniques [64][65][66]. It was found that: when the fluorinated unit content was low, the entropic force may dominate the surface structure since the random coil conformation in the solution can greatly affect the final conformation of the copolymer chains at the surface; when the fluorinated unit content was high, the enthalpic force may dominate the surface structure since the fluorinated moieties were prone to segregate to the surface [64].…”

“…It was found that: when the fluorinated unit content was low, the entropic force may dominate the surface structure since the random coil conformation in the solution can greatly affect the final conformation of the copolymer chains at the surface; when the fluorinated unit content was high, the enthalpic force may dominate the surface structure since the fluorinated moieties were prone to segregate to the surface [64]. Besides, the effects of different solvents and the film-forming methods were also discussed [65,66].…”

Surface segregation of fluorinated moieties on poly(methyl methacrylate-ran-2-perfluorooctylethyl methacrylate) films during film formation: Entropic or enthalpic influences

“…It was reported that the chain shapes or the conformations of polymers in solutions could affect the structures and properties of the polymers in bulk [22,23]. The influence of the preparation methods on the surface properties of fluorinated polymers has been reported in several publications [21,[24][25][26][27][28][29] and it was found that various surface structures can be obtained by controlling film-formation conditions such as the solvent species and preparation methods. When methyl methacrylate (MMA) and 2-perfluorooctylethyl methacrylate (FMA) block copolymer (PMMA-b-PFMA) film was prepared from its micelle solution with PMMA block as micelle corona and PFMA block as 0021-9797/$ -see front matter Ó 2010 Elsevier Inc. All rights reserved.…”

“…It was reported by our group that a relatively perfect close-packed and well-ordered structure of the perfluoroalkyl side chains at the surface of end-capped poly(methyl methacrylate) film was formed when the film was cast from a benzotrifluoride solution as opposed to being cast from cyclohexanone and toluene solutions [21]. Compared to perfluorinated block polymers [27], a contrary result was obtained when our group investigated the relationship between film-forming methods and the solid surface structure of random copolymers composed of butyl methacrylate (BMA) and dodecafluorheptyl methylacrylate (DFHMA) [24]. The water and paraffin oil contact angles for films by spin coating were higher than those by solution casting.…”